A Belle River, Ont., woman is wondering if she wronged a mayfly in a previous life, after a plague of them descended like "a sheet of blackness" on her suburban driveway.

Kelly Rivard screamed when she woke up to an infestation of the bugs, also known as fish flies in some regions, and enlisted her husband, Sylvain, to go into battle with a pressure washer.

A video of him clearing the driveway — with his shirt covering his nose from the fishy smell — is going viral on Facebook, with more than 1.2 million views and 7,000 shares as of Monday evening.

"Oh my goodness, that is crazy," Kelly Rivard can be heard saying over the roar of the pressure washer, disgust thick in her voice like the bugs piled up on her property.

It's unclear how many mayflies Rivard's husband had to reckon with, but they covered half of her driveway and filled three-and-a-half industrial-sized garbage bags. Several days later the smell still lingers. 

"It was bad, the smell was just atrocious. I mean, it still smells at the driveway now," said Rivard. "It was a blanket of them. And you could see the wings. My lawn was just fluttering. It was just awful. It's gross."

Mayflies are winged aquatic insects about three centimetres long. Their flying, adult lifespan lasts less than two days — long enough to mate and die. While the female insects die off above water, the males fly inland to die. 

Sylvain and Kelly Rivard

Sylvain and Kelly Rivard have become celebrities of sorts with their video of the mayflies getting more than a million views. (Sylvain and Kelly Rivard)

The annual invasion of the bug-eyed pests is a good sign, said Jeff Schaeffer, a biologist with the Great Lakes Science Center. They're an important source of food for fish, especially the varieties people like to eat.

The scientist did his dissertation on the insects and said there was a period from the 1950s to the 1980s where mayflies all but disappeared.

"Their return was actually seen as a very positive thing by virtually all the biologists, although we do apologize to the coastal residents," he said, laughing. "This is the price you pay for living in the middle of a healthy ecosystem."

Fish flies in Gimli

Scientists consider mayfly infestations a good sign. (Meagan Fiddler/CBC)

Rivard doesn't mind doing her bit for the environment, but wonders why the fish flies swarmed her driveway.

Schaeffer suspects it could be something as simple as the colour of the concrete on the driveway.

"That was a very heavy concentration," he said. "It could be a matter of lighting, the weather conditions on the night those flies emerged from the lake or there could be just a lot of them this year."

Turn off the lights and hope for the best

The biologist said the best way to avoid having your home overrun by fish flies is to turn off any outdoor lights and close the curtains.

Even if people take those steps, there's no saying whether crowds of the confused insects will descend on their house and select it as their final resting place. Still, Schaeffer said that crunch of dead bugs beneath people's feet is something they should be thankful for.

"Every time you see a mayfly you should be reminded that having them around is a good thing," he said. "Except for that one week a year."

Internet sensation

Rivard has become something of a celebrity. She's been bombarded with Facebook messages and more than 120 friend requests. She went into a hardware store Monday, and three of the five employees had seen the video on Facebook.

"I'm stunned. I can't believe it and I just think to myself why? I mean, it's fish flies," said Rivard. "I told someone that I think they're out in a vengeance for me. Maybe I did something to them in a prior life."